The present invention relates to a novel embodiment of a vibration proof lamp that is particularly intended for use under demanding operating conditions and is easier to manufacture compared with prior art embodiments. The present invention relates also to a method for manufacturing a vibration proof lamp. The present invention of a vibration proof lamp can be used on vehicles such as cars, busses, trucks, farm tractors, boats, aeroplanes or other mobile devices.
A general durability problem with lamps used on mobile devices such as motorized vehicles is that they are subject to vibrations of the vehicles. There are many reasons for the vibration. The vibration of a motor vehicle is a sum of vibrations caused by the running engine, air resistance, roughness of the road surface and also the running hydraulic motor and other vibration causing factors.
Under demanding operating conditions with e.g. mobile vehicles the source of the light in the lamp units used generally is a bulb which has an incandescent filament. In order to generate light the filament must be glowing under which condition the filament is very sensitive to all kinds of vibrations. The longer the incandescent bulb has been used the more fragile it is and the more easily the filament breaks.
The incandescent filament of the bulb used as the light source has a certain natural resonance frequency. If the frequency of the externally caused vibration is the same as the natural resonance frequency of the filament the amplitude of the vibration required to break the filament is not large.
Another stressing factor for the lamp is the heat inside the lamp unit which is generated by the incandescent bulb. If the reflecting part itself or some other part is made of e.g. plastic the heat causes damage to the construction itself or to the surface of the reflector.
In the following the prior art technique is described using the accompanying figures, in which
FIG. 1 shows a lamp unit embodiment according to the prior art,
FIG. 2 shows another lamp unit embodiment according to the prior art.
FIG. 1 shows the lamp unit embodiment according to the prior art. The prior art lamp unit embodiment consists of a reflector 1, a front glass 2, a seat mean 3, a bulb 4, a lamp housing 5 and resilient gaskets 6,7. The lamp unit embodiment is attached to the vehicle 9 with a bracket 8 and resilient washers 10, 11.
The reflector part 1 can be made of either plastic or metal. Plastic is used generally, because a better reflection effect is achieved by it. The front glass 2, which is in most cases glass or plastic is attached to the reflector 1. In the embodiment according to the prior art presented the resilient gasket 6 has been utilized to prevent damaging the parts 1, 2 and for absorbing the vibration.
The seat mean 3 on which the bulb 4 can be mounted and locked is attached to the reflector 1 of the lamp unit. The seat mean is usually fixedly attached to the reflector 1 with e.g. screws or locking plates.
After this the aforementioned assembly 1-4 presented is mounted inside the lamp housing member 5 so that the gasket 7 remains between the lamp housing and the aforementioned assembly. The gaskets 6, 7 prevent dirt getting into the lamp unit and their secondary function is to absorb mechanical vibrations. The reflector 1 and the front glass 2 are usually connected to the lamp housing member 5 by screws.
The lamp assembly 1-5 according to the prior art is attached to the bracket 8 using a bolt and vibration absorbing resilient washers 10, 11. The vibration absorbing washers 11 are located on both sides of the lamp housing member 5. It is also common that the inner vibration absorbing resilient washer 10 has been removed and only the washer 11 outside the lamp housing member 5 is used. The bracket 8, whereas, is fastened tightly using a bolt or a corresponding device to part 9 of the frame of the vehicle, e.g. to the bumper. The vibration of the lamp assembly 1-5 caused by air flow is not isolated by the resilient washers 10,11.
Under demanding operating conditions the prior art embodiment presented has the problem that the fastening of the bracket 8 at its both ends to the lamp housing part 5 and to the part 9 of the car must be very strong.
When the vehicle is moving the air flow causes a great torsional moment to both fixing positions as well as the different frequencies and amplitudes of the vibration. These factors make the absorption of the aforedescribed vibration difficult. However, the lamp housing part 5 itself must be fastened very firmly to the part 9 of the vehicle in order that it under usage would maintain its desired position.
In the lamp unit according to the prior art described above the heat generated by the incandescent bulb and its slow conduction out of the lamp unit causes additional problems. The heat generated damages both the reflector 1 and the lamp housing part 5.
FIG. 2 shows another lamp unit embodiment according to the prior art. The other lamp unit embodiment according to the prior art consists of a main reflector part 12, a seat mean 3 for the incandescent bulb, a front glass 2, a bulb 4, a lamp housing part 5 and vibration absorbing pads 13, 14. The purpose of the vibration absorbing pads is to absorb the adverse vibrations so that they cannot cause damage to the bulb 4 and to the seat mean of the bulb 3 through the lamp unit housing part 5, the front glass 2 and the reflector 12.
In U.S. Pat. No. 5,491,619 is also shown a lamp unit embodiment according to the prior art, which consists of a vibration and shock isolated mounting system. The lamp unit construction according to the prior art consists of a heat conducting metal element, which is positioned in heat conducting contact with the bulb. In that lamp unit construction four silicone rubber grommets or pads are placed one in each corner around the projecting center socket and the construction is locked with a locking plate to the socket. The lamp construction can be connected either to the reflector or to the lamp housing.
The greatest disadvantage of the lamp unit embodiment shown in U.S. Pat. No. 5,491,619 is that if the silicone pad is embedded in the lamp seat mean by casting so the seat mean of the bolt must be mounted separately on the sockets and must be locked using the locking plates. If the silicone grommets or pads are separate still an additional manufacturing phase is required. The presented embodiment according to the prior art requires always an additional assembly because the embedding in place by casting cannot be accomplished.
The purpose of the present invention is to produce such a vibration proof lamp unit embodiment which can be used especially under demanding operating conditions and which is easier to manufacture than the prior art embodiments and by which the problems presented above can be resolved and the draw backs can be corrected and the purpose is to show a method for manufacturing the vibration proof lamp unit in question. In order to accomplish this the vibration proof lamp unit embodiment is characterized in that the lamp unit comprises additionally a casting, vibration absorbing support posts, a seat mean of the bulb, casting channels and the protrusions of the bulb seat mean so that the seat mean of the bulb is vulcanized together with the lamp housing part by the help of the protrusions of the bulb seat mean and the vibration absorbing support posts are connected to both the lamp housing and the seat mean of the bulb by casting. In addition the method according to the present invention to manufacture a vibration proof lamp unit is characterized in that the method comprises a seat mean of the bulb, a mould for casting and a lamp housing part so that the seat mean of the bulb is placed in the mould so that the protrusions of the bulb seat mean remain between the frames of the mould, the mould is sunk to the desired depth into the lamp housing, the mould frame is cast with the casting mass, which forms through the casting channels the vibration absorbing support posts.